Systems and networks for transmitting information are well known and are often classified according to the size of the coverage area of the respective system or network. As one example, a wide area network (WAN) may provide coverage over a wide area, for example over an entire a city, state, or region of a country. Conventional cellular communication systems are one example of a WAN. Other networks may extend coverage only to smaller, localized regions and are referred to as local area networks (LANs). For example, a wireless local area network (WLAN) may provide wireless coverage to users within a particular building, or over a college or business campus.
Mobile stations, for example cellular telephones, often need to operate in both types of networks and, therefore, must also have the ability to transition between different types of networks. For example, a mobile station may operate in a WLAN while within a specific room because it is more economical to use a WLAN in that particular setting. However, as the mobile station reaches the limit of the coverage area of the WLAN (e.g., at the edge of the room), the mobile station needs to transition to the WAN in order to maintain unbroken communications.
Mobile stations often have a preferred network, service provider, and/or radio access technology (RAT). The preferred choice often depends upon the cost of the service or other service benefits. In one example, the mobile station may connect to the WLAN when inside an enclosed area, such as a room or office, but then transition to a WAN as the mobile station leaves the enclosed area.
Conventional multimode mobile stations are almost always battery powered and can consume a great deal of energy searching for WAN service while still operating in a WLAN. The station must account for the possibility that it may be on the edge of WLAN coverage and should therefore be ready for a WLAN to WAN handoff at any time. Since initial acquisition is often a time consuming processing, taking many seconds per failed attempt and often multiple seconds for successful attempts, the station must continuously look for WAN service at a minimum across several different channels and possibly multiple RATs as well. In conventional systems, if the acquired RAT or service provider is not the first choice, the station often continues to scan, in hopes of finding a higher, more preferred choice. If the WLAN is the preferred system of the mobile station, even after WAN service has been found, the mobile station must do periodic scans to keep information updated until WLAN coverage degrades to the point where a handoff from the WLAN to the WAN occurs. Such constant scanning by the mobile station wastes the energy of the battery of the station and also consumes valuable processing time that could be used for other purposes.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.